Spawning activity of early and late spawning rainbow trout (Oncorhynchus mykiss) strains under light program conditions
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, Aquaflow ref. :
TL2003-144
The seasonality of reproduction in rainbow trout is
based on the change in daylight length over the course of a year. From a
practical point of view it is desirable to have the fish spawn at a
predetermined time or more than once per year. The objective of the present
study was the characterisation of spawning activity in two different strains
of rainbow trout - one early and one late spawning - both under natural and
under controlled light and temperature conditions.
The investigation was conducted at the experimental
farm of Göttingen University at Relliehausen. Sexually immature fish from
both strains were either kept in outdoor circular tanks under natural light
and temperature conditions or indoors at a constant water temperature of 11±1°C
and an artificial 6-month light cycle consisting of 3 months of short (8h
light) and 3 months of long days (16h light). Over a two-year period, two
spawning seasons (under outdoor conditions) and three spawning seasons
(under light program conditions), were observed. Only female fish were taken
into consideration. As soon as they grew sexually mature, their respective
spawning periods as well the number and appearance of eggs produced and
their fertilisation rates were assessed.
Regardless of external stimuli, sexual maturity was
reached at age 3 years in the early spawning strain and 3.5 (light program
conditions) or 4 years (outdoor conditions) in the late spawning strain. The
6-month light program was particularly successful in advancing sexual
maturity in late spawners. In both strains, the 6-month light programme
enhanced egg yield. Due to differences in the time of puberty, under light
program conditions early spawners were stripped 2.3 times, late spawners 2.0
times. Under outdoor conditions, early spawners were stripped 1.6 times,
late spawners 1.3 times. Outdoors the period during which the majority of
females spawned, differed by up to two months between strains. Under light
program conditions, this difference was reduced to merely two weeks. The
length of the spawning season was equally reduced for both strains by their
being exposed to light program conditions (from 15 to 17 weeks to 8 to 12
weeks). Under both natural and controlled conditions early spawners had
superior fertilisation rates. Egg quality, therefore, appears to be
primarily a matter of genetic strain rather than of environmental factors.
It may be concluded that consecutive 6-month light
cycles, starting at a suitable time, offers the possibility to advance
puberty, increase productivity and make better use of production capacities.
Apparently there are differences between individual rainbow trout strains as
to their suitability to function under light program conditions as indicated
by the difference in response of early and late spawners.
Dissertation (ISBN 3-89873-533-8) by Dr. Nina
Wildenhayn.
For more information, contact:
HOLTZ
Wolfgang
Georg-August-Universität Göttingen - Institut für Tierzucht und
Haustiergenetik
Albrecht-Thaer-Weg 3
D-37075 Göttingen
Germany
Phone : +49 551 395605
Fax : +49 551 395587
e-mail: wholtz@gwdg.de